1. Field of the Invention
The present invention relates to a light source apparatus using lasers and a phosphor, and in particular, relates to a light source apparatus that emits visible light such as red, green, and blue light to be used in an image display apparatus, and also to an image display apparatus using the light source apparatus.
2. Description of the Background Art
Today, a projector is widely used as an image display apparatus that projects various video images and the like onto a screen in an enlarged manner. The projector causes a spatial light modulation device, such as a digital micromirror device (DMD) or a liquid crystal display device, to collect the light emitted from a light source, and causes the light modulated with a video signal and emitted from the spatial light modulation device, to be displayed as a color video image on the screen.
To obtain a bright large-screen video image in the projector, a high-pressure mercury lamp having a high brightness is used as a light source. The use, however, of a high-pressure mercury lamp as a light source has an environmental problem that hazardous mercury is contained, and also causes a problem that a short lifetime of the light source complicates the maintenance.
To solve the problems, a proposal is made for a light source apparatus using a solid light source, such as light-emitting diodes (LED) or lasers, instead of a high-pressure mercury lamp, and also for a new image display apparatus using the light source apparatus.
Lasers have a longer lifetime than a high-pressure mercury lamp. Further, the laser light emitted from the laser light source is coherent light, which therefore has highly directional properties and a high light-use efficiency. Furthermore, the laser light can ensure a wide color gamut due to its monochromaticity. Thus, the use of lasers of three colors, namely red lasers, green lasers, and blue lasers, provides a very bright light source apparatus, which can be applied to a high-brightness and full-color image display apparatus.
Due to its high coherence, however, the laser light causes speckle noise, which results in the deterioration of the image quality. In particular, laser light in the green and yellow wavelength regions, which has a high luminosity factor for human eye, has a major problem that the image quality deteriorates due to speckle noise.
In contrast, in an LED light source, which has a long lifetime, speckle noise as described above is not problematic. The present circumstance, however, is that the light source has a large emission area and a low light density, which makes it difficult to obtain a high-brightness image display apparatus.